Embodiments of the system relate generally to an electric power system and more specifically to protection systems for the electric power system.
Many power system monitoring, protection, and control functions could be performed more efficiently and accurately if power system digital measurements at multiple locations were synchronized. Generally such measurements are only somewhat synchronized because of difficulty in accurately synchronizing sampling clocks physically separated by large distances. Conventional uses of digital communications to synchronize sampling clocks at remote locations have accuracies limited by uncertainties in the message delivery time. In particular, digital communications can have different delays in different directions between a pair of locations which lead to an error in clock synchronization.
In addition to being important for multi-terminal transmission lines, clock synchronization is important in many other applications such as power relays, determinations of sequences of events, economic power dispatch, and any other situation requiring synchronization of clocks. Utilizing geographical positioning system (GPS) is one solution, however, it needs additional hardware and increases cost. Communication between various terminals at various locations is another solution; however, the main challenge in communication is caused by a clock rollover. Generally the clocks utilized are with a limited number of bits to save communication bandwidth which puts a limit on maximum time the clock can measure. Since the clocks have limits on maximum time, it results in independent clock rollovers which make multi-terminal clocks converge to a stable but non-synchronized status in which clocks are evenly dispersed along the whole clock range.
For these and other reasons, there is a need for an improved differential protection system.